SOURCE: American College of Sports Medicine, news release, Nov. 1, 201111/7/2011MONDAY, Nov. 7 (HealthDay News) -- Good news for high-mileage runners: They may be able to help themselves to an extra serving at holiday meals because variations in diet are less likely to affect them, researcher say.

The new study included nearly 107,000 runners who were grouped according to the distance they run each day: less than 1.2 miles (under 2 kilometers [km]); 1.2 to 2.4 miles (2 to 4 km); 2.4 to 3.7 miles (4 to 6 km); 3.7 to nearly 5 miles (6 to 8 km); and about 5 miles (8 km) or more.

The researchers found that body mass index and waist circumference increased significantly among the least active runners when they ate more meat and less fruit. But the effects of this diet change were reduced by 50 percent or more in the most active runners. The effects in runners who covered more than 1.2 miles a day were also reduced, but not to the same extent as the highest-mileage runners.

The study is published in the November issue of the journal Medicine & Science in Sports & Exercise.

"Generally, body mass index and waist circumference increase as a person eats more meat and less fruit," study author Paul Williams, a researcher at the U.S. government's Lawrence Berkeley National Laboratory, said in news release from the American College of Sports Medicine.

"My analysis indicates that this relationship weakens as runners increase their daily mileage. It appears that the more miles a person logs each week, the less affected they are by variances in their diet," Williams added.

The reasons could include increased fat burn associated with high levels of exercise or the fact that higher-mileage runners may be better at balancing their diet.

"My observations suggest that runners who exceed the recommended Physical Activity Guidelines for Americans can reduce their risk of gaining weight from high-risk diets, those with high meat and low fruit content," Williams said. "We have other data suggesting this benefit may also apply to walking."

More information

The U.S. Department of Health and Human Services has more about the physical activity guidelines for Americans at Health.gov.